1. Field of the invention
The present invention relates to a hand drill guide for use in firmly supporting a hand drill during operation and, more important so, ensuring that the drill bit is perpendicular at all times to the surface of the member being drilled, being a wall, a floor, a ceiling, a sheet, a plank or any similar member having a flat outer surface.
More particularly, the invention is concerned with an improvement to the drill guide disclosed and claimed in U.S. Pat. No. 4,179,231 issued on Dec. 18, 1979 to the same inventor.
2. Description of the prior art
The above mentioned U.S. Pat. No. 4,179,231 discloses a hand drill guide comprising an annular base around which a plurality of telescopic legs are distributed. Each leg comprises a hollow cylinder in which is slidably mounted a rod provided with a retaining head at one end. The rod with its head acts as a piston that is snugly mounted in the cylinder. One end of the cylinder is closed and fixed to the base from which it projects perpendicularly. The other end of the cylinder is open and defines an annular seat for the piston, the rod extending of course out of the cylinder through this annular seat. The hand drill guide also comprises an annular positioning head which is secured to the free ends of the rods. This head is intended to be applied firmly against the surface of the member to be drilled. The hand drill guide further comprises a drill holding assembly provided with a centering receptable into which may be inserted the chuck of a hand drill. The drill holding assembly is mounted selectively at one of several possible locations along the cylinders depending on the size of drill bit being used. Finally, each cylinder contains one spring that presses the piston-shaped rod firmly on the cylinder seat when the hand drill guide is idle. In use, force is applied on the hand drill which has its collar and chuck lodged into the aforesaid centering receptacle of the holding assembly fixed to the cylinders. This force thus moves the cylinders, the drill holding assembly and the base bodily toward the member to be drilled and drives the drill bit into it against the bias of the springs in the cylinders acting on the piston-shaped rods.
This hand drill guide is rather efficient in use. However, it has been found in practise that its structure should be improved to increase its stability when its telescopic legs are fully extended at the start of the drilling operation. In this extended position, there is indeed a lack of proper lateral support for the piston-shaped rods in the cylinders whatever be the thickness of the solid ring used as piston-head. This instability is more particularly due to the necessary considerable difference in axial length between the rods outside the cylinders and the retaining rings acting as piston heads inside the same. Wobbling or joggling is quite heavy when drilling is started and it decreases gradually to become acceptable only after the rod heads have moved to an appreciable distance from their annular seats at which time the rods attain a more important leverage action.
Another inconvenience with the head drill guide disclosed and claimed in the prior patent is that there is no positive way to ensure that the center of the annular position head, applied against the member to be drilled, lies directly over the point where the hole is to be drilled. Therefore, it is necessary in practise to proceed by trial and error.